The octane requirement increase effect exhibited by internal combustion engines, e.g., spark ignition engines, is well known in the art. This effect may be described as the tendency for an initially new or relatively clean engine to require higher octane quality fuel as operating time accumulates, and is coincidental with the formation of deposits in the region of the combustion chamber of the engine.
During the initial operation of a new or clean engine, a gradual increase in octane requirement, i.e., fuel octane number required for knock-free operation, is observed with an increasing build up of combustion chamber deposits until a stable or equilibrium octane requirement level is reached. This level appears to correspond to a point in time when the quantity of deposit accumulation on the combustion chamber and valve surfaces no longer increases but remains relatively constant. This so-called "equilibrium value" is normally reached between 3,000 and 20,000 miles or corresponding hours of operation. The actual equilibrium value of this increase can vary with engine design and even with individual engines of the same design; however, in almost all cases, the increase appears to be significant, with octane requirement increase values ranging from about 2 to about 10 research octane numbers being commonly observed in modern engines.
The accumulation of deposits on the intake valves of internal combustion engines also presents problems. The accumulation of such deposits is characterized by overall poor driveability including hard starting, stalls, and stumbles during acceleration and rough engine idle.
Many additives are known which can be added to hydrocarbon fuels to prevent or reduce deposit formation, or remove or modify formed deposits, in the combustion chamber and on adjacent surfaces such as intake valves, ports, and spark plugs, which in turn causes a decrease in octane requirement.
Continued improvements in the design of internal combustion engines, e.g., fuel injection and carburetor engines, bring changes to the environment of such engines thereby creating a continuing need for new additives to control the problem of inlet system deposits and to improve driveability which is usually related to deposits.
It would be an advantage to have an additive concentrate which produces a rapid and substantial octane requirement reduction response.